Is it possible to use adb or fastboot on a phone completely hard bricked?

[TheSecondComing]

When I say completely, it's literal, as even the recovery is inaccessible...

 

[tecknight]

No, unfortunately it is not possible. The only possible way to recover would be from EDL (Emergency Download Mode), which requires manufacturer specific drivers and encryption keys.
If your phone is an Xiaomi, you are probably in luck, as Xiaomi provides EDL recovery tools for most of their phones.
However, they are the only manufacturer that I know of that does this.
Good luck my friend